Static Loops :    18


library ieee;
use ieee.std_logic_1164.all;
entity parity is

  port (
    a : in  std_ulogic_vector(7 downto 0);
    y : out std_ulogic);

end parity;

Note the use of std_ulogic. Be wary of the use of std_ulogic as the resolution function does not treat 'Z' as a special case.